Large programmable coefficient of thermal expansion in additively manufactured bi-material mechanical metamaterial

Abstract

ABSTRACT The current metamaterials with the programmable coefficient of thermal expansion (CTE) usually present the unexpected anisotropy, and the experimentally measured CTEs are quite narrower. Here, a bi-material metamaterial was constructed. The material extrusion process was established to fabricate the metamaterial. The measured CTEs in various in-plane directions are in good consistency to each other, experimentally verifying the identical CTE in various in-plane directions. The relative deviation between the experimental measurements and theoretical predictions is within −13.0% to +11.0%. The positive programmable CTEs are as high as 204 and 258 ppm/°C, which are larger than those of the basic polymers nylon and polyvinyl alcohol (PVA). Otherwise, the negative CTEs of −25 and −77 ppm/°C are obtained, even though both the nylon and PVA have positive CTEs. The programmable CTEs are expanded to be [−77, +258] ppm/°C, far beyond the literature results, supplementing the additive manufacturing and experimental basis to the engineering applications.